Windows only: Windows utility TweakNow puts a friendly interface on the most common registry settings on your PC, complete with an Undo button. Tweak your Start menu, Control Panel, Desktop, user accounts, and other settings using TweakNow, which shields you from the decidedly not-fun and risky undertaking that is editing the registry by hand. This looks particularly useful for locking down a PC for the kids—for instance, you can use it to disable access to the Control Panel and desktop context menus. TweakNow is a free download for non-commercial use, Windows only.